Piezoelectric lead zirconate titanate ceramic with chromium and thorium additives



United States Patent O ABSTRACT OF THE. DISCLOSURE A piezoelectric ceramic composition having a solid solution of lead zirconate titanate stannate as a base and additional constituents ofsmall quantities of thorium oxide and chromium oxide. The ceramic composition has a greatly enhanced electromechanical coupling factor and a high mechanical. quality factor, as well.

This application is a continuation-in-part of application Ser. No. 349,323, filed Mar. 4, 1964, and now abandoned.

The present invention relates to piezoelectric ceramic "compositions and, more-particularly, to a novel piezoelectric ceramic material comprised of lead'titanate zirconate -stannate in which certain additional constituents are added to'greatly enhance the electromechanical coupling factor and the high mechanical quality factor of the composition.

As is well known, lead titanate zirconate stannate piezoelectric materials, which are solid solutions composed of lead titanate PbTiO lead zirconate PbZrO and lead stannate PbSnO exhibit superior piezoelectric characteristics in comparison with other oxide ferroelectric substances, such as barium titanate.

Thefundamental parameters for evaluating the piezoelectric properties of a piezoelectric material are the electromechanical coupling factor and the mechanical quality factor. The former is an indication of the efliciency of transforming the electric oscillation into mechanical vibration and conversely, of transforming the mechanical vibrationinto electricv oscillation. Thus, the higher'the electromechanical coupling factor, the better the efiiciency of conversion.

The mechanical quality factor is in the inverse proportion to energy consumed by the composition during the energy conversion. Larger-"mechanical quality factors indicatersmaller energy consumption, and vice versa.

One 'of the areas of application ofpiezoelectric compositions. isthe manufacture. of ceramic filter elements. In manufacturing such elements, it is necessary to furnish an electromechanical coupling factor with an optimum ..:value selected from a widerange, and it is desirable for the mechanical quality factor to be as great as possible. This is described in an article by Macario entitled, Design Data for Band-Pass Ladder Filters Employing Ceramic Resonators, Electronic Engineering, vol. 33 (1961), No. 3, pages 171-177.

In transducer elements of mechanicalfilters, it is necessary that both the electromechanicalcoupling factor and the mechanical quality factor be aslarge as possible.

The'Kulcsar U.S. Patent 3,264,217 suggests the use of thorium additives in improving the electromechanical coupling factor of piezoelectric ceramic elementsIThe "Jafie et al. U.S'. Patent No. 3,216,943, on the other hand,

suggests the use -of chromium additives'to improvethe mechanical quality factor of 'the same piezoelectric ceramic elements. Howeven'thethorium and chromium additives, when used individually, have adverse effects provide a piezoelectric material having a unique composition enhancing boththe electromechanical coupling factor and the mechanical quality factor.

Still another object of the instant invention is to'provide a novel piezoelectric material oflead titanate zirconatestannate compositions which contain two additional constituents that are added in order to enhance both the electromechanical coupling factor and the mechanical quality factor.

Still another object of the instant invention is to provide a novel piezoelectric material" formed "of. a' lead titanate .zirconate stannate composition and having thorium oxide 'and chromium oxide added thereto to greatly enhance both the electromechanical coupling factor and the mechanical quality factor.

Still a further object of the invention is to: provide: a novel piezoelectric material having a lead titanate zirconate stannate composition wherein a portion ofthe lead is substituted for by barium,*strontium, orlcalcium.

These and other objects of the invention'willbecome more apparent when reading the accompanying specifications.

The compositions of this invention contain: a solid solution of lead zirconate, lead titanate, and leadstannate, which may be represented by'Pb(Zr 'I i Sn ')O Additionalconstituents of thorium oxide and chromium oxide are provided to enhance themechanical quality factor and electromechanical coupling factor of the compositions.

The ranges for x, y and z are restricted to x=0.00-0.90, y=0.10-0.60, and z=0.00-0.65,

wherein the total of x, y and z is equal to 1.0.

Compositions falling outside this range do not have electromechanical coupling factors of suflicient -magnitude to provide efiicientpiezoelectric ceramiczelements for'transducers of mechanical filters.

.tainable in cases Where x,

The largest electromechanical coupling-factor is oby and z are in the'range of 0.52-0.53, 0.48-0.47 and 0.00, respectively.

The excellent piezoelectric properties available'in'the materials described above are not diminished, even ifat least one member of. the group consisting of barium (Ba), strontium -(Sr), and calcium '(Ca). is substituted for up "to 25. atom percent of the lead content of the basic composition.

. The amount of thorium dioxide present may vary from 0,05 wt. percent to 5.0 'wtpercent, while the amount of chromium oxidei may vary from'0.01-wt...percent to 0.30 wt. percent.

The invention will be explained in detail in the following examples:

Example I A basic composition (represented bythe formula Pb(Zr ;Ti O i.e., x=0.'54,-y='0.-46,and z'=0.00)

'was prepared by mixing a powder consisting of 50'mol percent lead monoxide dioxide (ZrO '(PbO), 27 mol' percent zirconium and 23 'mol percent titanium dioxide (TiO Varying amounts of'thorium dioxide'and chromium oxide were added to'the mixture. The amount of thorium dioxide never exceeded 5.0%,While the addition of chromium oxide never exceeded 0.30 Wt. percent. Some samples contained no thorium oxide. Other samples contained no chromium oxide; while still other samples prepared contained varyin mixtures of thorium and chromium oxide. All of the constituents were mixed in a ball mill, and the mixed powder of each respective composition mentioned above was presintered at 900 C. for approximately one hour, crushed, press-molded into discs and sintered at 1300 C. for an hour. The resulting ceramic discs were provided with silver electrodes and were piezoelectrically activated at 100 C. for an hour by means of an applied electric field of 50 kv./ cm. After standing for 24 hours, the electromechanical coupling factor for the radial mode vibration (hereinafter, referred to as K and the mechanical quality factor (hereinafter referred to as Q were measured to evaluate the piezoelectric activities. The results obtained are shown in Table I.

TABLE I Composition, Wt. Percent K No. (per- Qm Th: CHO: cent) 1-.... Pb(Zro.s-1Tlu4o,)0s 48 300 54Tio.4s)0a--.-. 51 105 o.s4Tio.-n)0s. 58 90 Pb o.s4Tio.4s) 03. 62 9O o.s4 lu 400s- 61 90 b( ro.r4 1n 40) a. 60 90 o.siTin l6) s- 59 90 0.s4 io to) Os. 50 110 Pb(Z1'u 5. Tin 4003. 0 51 340 Pb(Zro.siTio.4e) 0s- 48 560 o.54 iu.ta) 0s- 50 880 o.54Tio.4s) O: 53 360 PMZrsmTims) Os- 57 110 Pb usiTiuAa) s 59, 110 l'0-5l 0-1 .0) O3. 59 110 o.54Tio.4e) a. 56 320 r0.51Ti0.46)03 63 110 Io.s4Tlu.4o) s. 55 820 Pb(Zro.uTiu.4s) 0a- 51 320 Pb 10 .siTio.4s) s- 32 270 Pb (ZIOMTinJs) 0a- 27 550 P 1'0.s4Tio.4s)Os 41 770 Pb o .u iu .n) 0:: 48 750 Pb(Z1o,stTlo,4e) 0:- +0. 30 40 680 The results of Nos. 1-8 showed that the incorporation of thorium dioxide by itself into the basic ceramic composition resulted in a marked increase in K while suffering a corresponding decrease in Q,,,.

The results of Nos. 9-19 showed that the addition of both thorium oxide and chromium oxide to the basic composition markedly iacreased Q while maintaining K, at an equivalent, or increased value as compared with the Q values obtained through the addition of thorium dioxide alone. The results of -24 showed that the unusual characteristics obtained by mixing both chromium and thorium oxide cannot be obtained by the addition of chromium oxide alone. The addition of chromium oxide, although increasing the mechanical quality factor, correspondingly decreases the electromechanical coupling factor.

In the event that the content of thorium oxide exceeds 5.0 wt. percent, or is less than 0.05 wt. percent, the improvement in characteristics is not obtained even if amounts of chromium oxide are added to the mixture. correspondingly, in the event that the content of chromium oxide exceeds 0.30 wt. percent, or is less than 0.01 wt. percent, the addition of thorium oxide does little to improve the piezoelectric characteristics of the basic composition.

The irnprovements made in the piezoelectric properties by the addition of both ThO and Cr O clearly result from the presence of both thorium and chromium ions. Thus, the thorium and chromium ions may be introduced into the basic composition by the use of the oxides or, in the alternative, may be introduced by means of compounds which are decomposed into oxides at elevated temperatures. In the case of thorium, thorium hydroxide, the compounds Th(0H) or the like may be used, and in the case of chromium, chromium sulfate, the compound Cr (SO or the like may be used.

In the event that such compounds are used, they should be utilized in amounts equivalent to the desired mol percent proportions obtained when using the oxides. The re- 4 sults obtained in subsequent examples were derived through processes outlined above withregard to the table of Example 2, unless otherwise recited.

Example 2 TABLE 2 Composition, 10 Wt. Percent Kr No. (pcr- Qm Th0 CHO; cent) 25.... Pb(Zln,soTlo,5u)Os 29 340 26...- Pb(Zru.5oTio.5o)0a +1.0 51 110 27...- Pb(Zro.5sTiu. 3.. +1.0 +0.20 47 459 20 28.... Pb(Zru.5zTio.4a) 3-. 45 350 29..-- Pb(Zru.:.2Tiu.4r)Oa.- 52 95 30 Pb(Zr0, zTi0.4s)Oa.. 58 360 31-.-. Pb(Zlo 5sTiu 44) 43 340 32.... Pb(Ztg 5sTlo. 3.- +1.() 6O 98 33...- Pb(Zl'0.58 i0Ai)03. +1. 0 +0. 20 56 364 Table 2 clearly shows that the change of the x and y parameters in the basic composition does not affect the improved piezoelectric activities obtained by utilizing thorium and chromium ions in combination with the basic composition.

Example 3 A basic composition was prepared according to-the procedure of Example 1 wherein x=0.49, y=0.46, and 1:005, and a second composition wherein x=0.44, y=0.46, and z=0.10.

w-t. percent of thorium oxide, or a mixture of 1.0 wt. percent of thorium with 0.2 wt. percent chromium oxide were added to the composition. The results obtained are outlined in Table 3.

Table 3 indicates the results obtained upon testing these discs. It clearly shows that the substitution of tin for a portion of the basic composition does not impair the piezoelectric properties, which are improved by the presence of thorium and chromium additives.

Example 4 Discs were prepared by the procedure outlined in Example 1, except that barium, strontium, or calcium were substituted for a part of the lead in the basic composition. Table 4 indicates the results obtained thereby.

TAB LE 4 Composition, Wt. Percent K.

No. (per- Qm Th0; CF10; cent) .44) O 47 270 T +1. 0 +0. 20 58 330 48 230 4 (Zr 0540310100: +1. 0 +0. 20 57 320 44. Pbo,lu l'o.05(ZI'0.NT10.46 I10.05)03 46 320 45. Pbom rosflzro.nTinnoS o .09 2... +1- 0 55 340 46-... PbmaCaunflZro.uTio.4s)Os 45 320 47..-- P .sC3o.0l(Zln.MTi0.4n) s +1.0 +0.20 56 300 It is clear that the substitution of one member ofthe group including barium, strontium, or calcium for a portion of the basic composition does not affect the piezoelectric properties, which are improved by the presence. of both thorium and chromium additives.

Additional amounts of either 1.0

Examples 1-4 clearly indicate that an improved piezoelectric material is provided by the addition of both thorium and chromium additives to a basic ceramic composition. The basic composition may be of a lead titanatelead zirconate solid solution or, in the alternative, may include a lead-stannate component. Furthermore, a portion of the lead in the solid solutions may be substituted for by at least one alkaline earth material.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited not by the specific disclosure herein, but only -by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A piezoelectric ceramic composition having the formula PB (Zr Ti Sn )O wherein y=0.100.60, and

z=0.00-O.65, the sum of x, y and 2 being equal to 1.00;

said composition incorporating chromium sesquioxide thorium dioxide in amounts of from 0.01 to 0.3 Weight percent chromium sesquioxide and from 0.05 to 0.5 weight percent thorium dioxide.

2. The composition of claim 1 wherein y=0.48-0.47, and

3. The composition of claim 1 wherein up to 25 atom percent of lead (Pb) is substituted for by at least one member of the group consisting of barium, strontium and calcium.

References Cited UNITED STATES PATENTS 20 TOBIAS E. LEVOW, Primary Examiner.

ROBERT D. EDMONDS, Examiner. 

